Pre-stressing of concrete assemblies



March 18, 1958 M. VAN BUREN 5,

PRE-STRESSING OF CONCRETE ASSEMBLIES Filed Nov. 8, 1954 vs Sheets-Sheet1 II II J I INVENTOR MYERS WA/BU/FE/V.

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Filed Nov. 8, 1954 United States Patent 2,826,800 PRE-STRESSING 0FCONCRETE ASSEMBLIES Myers Van Buren, Haworth, N. J., assignor to RaymondConcrete Pile Company, New York, N. Y., a corporation of New JerseyApplication November 8, 1954, Serial No. 467,392

3 Claims. (Cl. 25-118) This invention relates to methods and apparatusfor forming so-called pre-stressed concrete units and more particularlyto methods and apparatus capable of manufacturing a multiple number ofsuch units in end-to-end relationship so that a single stressingoperation is suflicient for all units in the group.

Various methods of forming pre-stressed concrete units are presently inuse, among them being the method for making hollow piles or pipedescribed in: U. S. Patent No. 2,609,586, granted to R. M. Parry onSeptember 9, 1952 which comprises running cables through holes providedin the walls of a series of concrete units and applying tension to theextremities of these cables by means of forces reacting against the endsof the assembly of units. The cables are thenbonded in place so that,when the tension applying means have been removed, the cables willremain under heavy tension and act to maintain the v concrete assemblyitself under compression, whereby the latter will manifest increasedstrength when subjected to torsional stress. To effect this bonding,grout is forced into the holes in the concrete units while the cables rice at the IOU-foot and ZOO-foot marks, thereby forming three 100-footpressed piles.

running therethrough are maintained under tension, the tension notbeingremoved from said cables until after the grout has set, thus permittingbonding the cables under tension throughout their length to theconcrete. Practice has shown that the labor costs in such a stressingoperation are almost entirely independent of the length of the assemblyto be stressed, that is for example, nearly as much labor is required tostress a 50-foot assembly of units as for one 250 feet long. Therefore,substantial economy in both cost and speed can be effected by aprocedure which calls for pre-tensioning an elongated concrete structureby a single stressing operation and j so as to form an elongatedstructure 22 which may be 1 sioning cables are run through alignedapertures provided in both the units and spacer means. T hereupon asingle post-stressing or tensioning and grouting operation is performedafter which, by virture of the spacer means, the cables may be readilysevered, the spacer means removed and a multiple number of pre-stressedconcrete assemblies thereby formed. For example, in the manufacture ofconcrete piles, when it is desired to manufacture relatively short pilesof for example 100 feet in,

length, a plurality of concrete units, each having the desiredcross-sectional size and configuration and together totaling 300 feet inlength are arranged in end-to-end.

relationship with spacers of the type described hereinafter, interposedbetween adjacent units at the 100-foot and 200- foot marks, therebyforming an elongated concrete structure. Both the units and the spacersare provided with aligned, cable receiving apertures intowhichtensiouing According to the invention herein, a spacer is providedOther and more specific objects, features and advantages of theinvention will appear from the detailed description given below, takenin connection with the accompanying drawings which form a part of thisspecification and illustrate by 'way of example the presently preferredembodiments 'of the invention.

'In the drawings? Fig. 1 is a plan view partly in cross-section, showinga plurality of tubular concrete units aligned in end-to-end relationshipin the process of being stressed with spacers v interposed betweenadjacent groups of units;

Fig. 2 is an enlarged side elevational view of one of the spacers ofFig. l;

Fig. 3 is a sectional view taken on the line 33 of a Fig. 2;

Fig. 4 is. a fragmentary sectional view taken on the line 4-4 of Fig.2;j

Fig. 5 is a sectional side elevationalview of the spacer of Fig. 3andfshowing the first step in the method of removing this spacer afterthe stressing operation has been completed;

Fig. 6 is a fragmentary side elevational view of a portion of the spacerof Fig. 2;

Fig. 7 is an enlarged, fragmentary, side elevational view 1 of a portionof the spacer of Fig. 2, showing one of the tensioning cables passingtherethrough;

Fig. 8 is a partial sectional view showing a portion of a modified formof spacer;

Fig. 9- is a sectional view taken on the line 99 of Fig. 8; and y Fig.10 is a fragmentary, sectional view of another modified form of spacer.

Referring now in more detail to the drawings and particularly to Fig. 1,according to the method of using the invention a plurality of concreteunits or groups of units 20 are arranged in end-to-end relationship withspacers 21 interposed between adjacent units (or groups of units) prestressed inits entirety by a single stressing operation. The concreteunits 20 in the form here shown are'tubular and. are provided with aplurality of circumferentially spaced cable-receiving apertures 23,extending longitudinally therethrough. In like manner, spacers 21, aswill be described more fully hereinafter, are provided with a 7corresponding number of similarly, circumferentially spaced, hollowtubes 24 which form cable-receiving apertures extending through thespacers.

In assembling the elongated concrete structure 22, the concrete unitsand spacers which constitute the same are arranged so that theircable-receiving apertures are aligned and so as to form cavitiesextending continuously through the elon gated structure 22,and-tensioning cables 25 are then threaded therethrough so that saidcables extend continuously through the entire elongated structure 22with Y the cable ends projecting from each end thereof. Cables 25 areeach formed of a plurality of Wires 29 which may be held apart in thedesired spaced relationship by cylin "drical wire spreaders 29' (Fig.7).

3 7 'At this stage of the procedure, the entire structure 22 comprisingamultiplicity of units :is subjected to' a stressing operation which maycorrespond to the operation described in said U. S. Patent No. 2,609,586in connection with a single group-of'concreteunits. Thus locking devices26, each comprised of mating'external.and'internal cones 27 and 28, areapplied to the'projecting ends'of the cables 25. The externalcone 27 isplaced'around the outside of the projecting ends of the cable wires.29While the internal cone 28 is inserted centrally ofisaid wires. Tensionis then applied evenly to the projecting ends of all cables by means ofpull-iacks 30 which latter react through external cones 27 against theopposite ends of the elongated concrete structure 22. When the desiredtension has been applied 'totthe cables, internal cones 28are forcedinwardly bymeans of jack means 31 thereby wedging the wires 29 of eachcable against the surfaces of external cones .27. The tension applyingpull-jacks are then released whereupon the wires of each of the cablesmay contract slightly, thereby drawing the inner cones 28 furtherinwardly into external cones and thus locking the wires, still undertension, between said cones. Each of the inner cones 28 is truncated andprovided with a longitudinally extending passage 32 designated to permitthe introduction of grout centrally ofthe wires 29 into the cavities inwhich the cables are disposed. After jacks 30 have been withdrawn, groutmay be forced in under pressure around the wires, thereby effectivelybonding the cables throughout their length to the concrete structure. Atthis point in the op eration the elongated concrete structure22has beenprestressed in its entirety, that is, since a heavy tension remains inthe cables which are in turn adhesively bonded to the concrete structurethe latter is maintained under compression. Thereafter, by severingcables 25 at those points in their lengths where they pass through thespacer units and removing those spacer units, a plurality of individualpre-slressed concrete structures are. obtained.

Referring now to Fig. 2, each spacer unit 21 is comprised of a pair ofspaced annular disks 33 and 34 respectively. These discs are releasablyand adjustably .secured together in spaced apart relation by a pluralityof bolts 35, and each disc is provided with a plurality ofcircumferentially spaced holes 36, 36 respectively, pairs of which areaxially aligned when the discs are bolted together. Slidably disposed ineach pair of aligned holes and extending between the discs of the spacerista hollow tube 37, the interior of which provides an aperture adaptedto permit passage through the spacer of one of the tensioning cables 25..The spacers 21 are designed to conform to the cross-sectional shape andsize of the particular concrete units which are to be stressed and thenumber and circumferential spacing of the tubes'37 in eachspacercorresponds to the number and spacing of the apertures formed in saidconcrete units, so that these tubes may be aligned with the apertures inthe concrete sections.

In initially assembling the elongated concrete structure 22, describedabove, two or more concrete units 20, or groups of such units, of thedesired length are arranged in end-to-end relationship, with adjacentunits being axially spaced apart a sufficient distance to permitinsertion of a spacer 21 therebetween. Laterally projecting arcuateflanges 38 and39, provided on the discs 33 and 34, respectively, of eachsuch spacer and corresponding in shape to the external surface of units20,

serve to center the spacers relative to the units. The spacers are thenangularly adjusted relative. to the units so as to align hollow tubes 37with the cable-receiving apertures, thereby providing continuouscavities extending through the entire concrete structure 22 for thereception of cables 25. Once this alignment has been achieved, means areprovided on each spacer to maintain the angular positioning of saidspacer relative to the concrete units. This retaining means consists ofa plurality tween discs 33 and '34 of each spacer. These assemblies areeach comprised of a pair of blocks 41, 42 having oppositely inclinedabutting surfaces 43, 44 each of which is formed with a cut-out portion45, 46, respectively, which cut-outs cooperate to form a taperedaperture extending through the assembly and designed to receive atapered pin 47. As shown, these blocks 41, 42 are held in positionbetween the discs 33, 34 by means of U-shaped wire braces 48, 49 weldedto the discs and adapted to slidably embrace the blocks on three sides.The braces 48, as shown in Fig. 4, are secured to discs 33 with :theopen end of the U facing radially outward of: said disc, while thebraces 49 are secured to disc 34 with the open end of the U facingradially inward of said disc. Wedge blocks 41, 42 are therefore adaptedto he slid radially from opposite directions through the openends of theU-shaped braces into and out of position between discs 33' and 34. Whenthe spacers 21 are initially interposed between adjacent concrete units20 as aforesaid, the blocks are positioned in their braces and thetapered pin 47 is lightly tapped part way into the aperture formedby'the cut-outs in the abuttingsurfaces 43, 44. After thespacer has beenangularly adjusted so that its hollow tubes are aligned with thecable-receiving apertures 24,

bolts 35 are removed or loosened and tapered pins 47 are driven firmlyinto the aperture extending through the assemblies 40, thereby keyingthe wedge blocks and assuring that assemblies 40 will have parallelexternal faces a definite distance apart. It should be noted that inorder to insure a uniform gripping relationship between the spacer discsand the adjacent concrete units, the outer sides of discs 33, 34 may beprovided with facings of compressed sheet asbestos 50, 51 bonded to saiddiscs by means of a suitable adhesive 52, 53, such as rubberbondedpacking means of some suitable well-known material (Fig. 7). With thespacers in this tight, gripping relationship with the units, maintenanceof the alignment of the hollow tubes 37 and apertures 24 throughout thestressing and grouting operation is assured.

After the stressing operation has been completed on the elongatedstructure 22 as described above, by then severing the tensioning cablesat the points where they pass through the spacers 21 and removing thespacers from between adjacent units, a plurality of pro-stressedindividual units (or groups of units) may be obtained. 'To accomplishthe above, it is necessary first to sever the hollow tubes 37 so as toprovide access to the cables 25. To this end,a burner torch 54 (Fig. 5)maybe provided to cut through these tubes 37, and the cables 25 may thensimilarly be severed by burning after the tubes have been cut in half.As soon as all of the tubes 37 of the spacer, together with the cablespassing therethrough have been severed as indicated at 55, the spacersmaybe removed from between adjacent concrete units, thereby leavingthose units completely separated and pre-stressed'as desired. When it isdesired to re-use spacers 21 for another stressing and groutingoperation, it will of course be necessary to replace the hollow tubes37. which have been destroyed by the burning operation. Once such a newset of tubes has been installed in a spacer, the same will be ready foruse once again in the above-described manner.

If it is desired to avoid the necessity of burning the spacer tubes inhalf in order to obtain access to the tensioningcables for severing thesame, the modified form of spacer 60: shown in Fig. 8 may be employed.This type of spacer comprises similarly spaced annular discs 61 and 62having aligned apertures 62', 63, but in place of the one-piece tubes'37of spacers 21,-the tubes 64 of this type spacer are .formed in two parts65, 66, each welded in position in the hole of the disc at which itbelongs. The spacing of the discs 61, 62 and the length of the tubeparts65, 66 are so designed asto provide a aes soo in! a) space 67between the ends of these tubes to permit relative movement therebetweenduring the procedure of inserting the spacer between adjacent concreteunits as has been described above. This space 67 between the tube partis closed by means of a split clamp 68 which is provided with a rubberlining 69 designed to form an efiective seal between the parts 65, 66,but also adapted to permit lateral sliding of the tube parts when thediscs of the spacer are expanded.

These spacers 60 may be employed in similar manner to spacers 21described above, that is, they are inserted between adjacent concretemembers 20, their tubes aligned with the cable-receiving holes of theunits and the stressing and grouting operation performed. After thegrout has set and it is desired to divide the elongated structure 22into individual pre-stressed units, the clamps 68 may be removed fromthe tubes 64, thereby providing access to the cables 25 through space67. These cables may then be severed by a conventional means, such assawing without destroying the tubes themselves. Therefore, the spacer 60remains intact in its entirety and may be re-used for an indefinitenumberof stressing operations. I

As described above, during the stressing operation, the hollow tubes ofthe spacers are aligned with the cablereceiving holes formed in theconcrete units, thereby forming cavities extending continuouslythroughout the elongated structure 22. When grout is introduced throughpassage 32 at one end of the elongated structure 22, it will be forcedinto these cavities throughout the length of the concrete structureitself. However, when it is desired to provide an additional grout entrypassage at intermediate points along the length of the elongatedstructure 22 so as to further insure a uniform dispersion of the grout,spacers of the type 60 may be provided with nipples 70, whichcommunicate with the opening 67 and thence the interior of tube parts65, 66. These nipples 70 may then be used to introduce additional groutthrough the spacers into the holes formed in the concrete units.

Referring now to Figure 10, a portion of an alternate embodiment of aspacer according to this invention is therein disclosed.- This spacer 70is comprised of a plurality of cylindrical plugs or blocks 80 havingcentral passages 81 formed therein, which are designed to be alignedwith the cable-receiving apertures 24 formed in the adjacent concreteunits. The number and location 81 of eachspacer 80 will, of course,coincide with the number of cable-receiving apertures provided in theconcrete units. These spacers 80 may be formed of a material such as iseasily cut or sawed, such as wood, wood fiberboard, plaster of paris,etc., so that after the stressing operation has been completed, asaforesaid, the tensioning cables units 20 by sawing first through thespacers 80 themselves and then through the cables. If desired, thespacers 80 can be formed of any material such as wood, which is capableof being removed by self-sustaining combus- 24 may be severed betweenadjacent concrete tion. 0n the other hand if desired, the spacers can beformed of a material which may be melted by the application of heat,such as sulfur, rosin and various thermosetting resins. In any event,spacers of this type 80 are designed for one use only, since after asingle stressing operation, as described above, these spacers 80 must bedestroyed to provide access to the tensioning cables for severing thesame.

The invention is particularly Well adapted for use in the economicalconstruction of concrete pipe as well as hollow concrete piles.

The invention is also adapted to be used in cases where the wire cablesare contained in metal sheaths such as shown in U. S. patent to UpsonNo. 2,677,957, granted May 11, 1954.

Although certain particular embodiments of the invention are hereindisclosed for purposes of explanation, various further modificationsthereof, after study of this specification, will be apparent to thoseskilled in the art to which the invention pertains. Reference shouldaccordingly be had to the appended claims in determining the scope ofthe invention.

What is claimed and desired to be secured by Letters Patent is:

'1. A re-usable spacer for use in the prestressing of a plurality ofconcrete units comprising a pair of spaced discs adjustably securedtogether, at least one hollow cable-receiving tube extending betweensaid discs, and wedging means interposed between said discs and adapted,when the spacer is interposed between adjacent concrete units to bestressed, to key said discs apart.

2. A re-usable spacer for use in the prestressing of a plurality ofconcrete units comprising a pair of spaced discs adjustably securedtogether, a pair of aligned apertures one in each disc, a hollowcable-receiving tube slidably received in said pair of aligned aperturesand extending between said discs, wedging means interposed between saiddiscs.

3. A re-usable spacer for use in the prestressing of a plurality ofconcrete units comprising a pair of spaced discs adjustably securedtogether, a pair of aligned apertures, one in each disc, a hollow tubeextending between said discs and connecting said apertures, said tubecomprising a pair of spaced tube parts, one secured to each discconcentrically with the aperture of said disc, and a removable clampslidably embracing said tube parts and extending across the spacetherebetween, and wedging means interposed between said discs.

References Cited in the file of this patent UNITED STATES PATENTS2,609,586 Parry Sept. 9, 1952 2,677,957 I Upson May 11, 1954 FOREIGNPATENTS 489,515 Canada Ian. 13, 1953 U. S. DEPARTMENT OF COMMERCE PATENTOFFICE CERTIFICATE OF CORRECTION Patent No, 2,826,800 Myers Van Buren Itis hereby certified that error appears in the printed specification ofthe above numbered patent requiring correction and that the said Letcers Patent should read as corrected below.

March, 18,- 1958 Column 1, line- 34, for "torsional stress" re'ad e-tensional stress,

Signed and sealed this 24th day of June 1958.,

Attest:

KARL HMAXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents

